1. Field of the Invention
This invention relates to a series of speed increasing gear and devices reduction gear employing an inscribed meshing planetary gear construction which is preferably utilized as a speed increasing gear or a reduction gear, more particularly, a small-sized speed increasing gear or a reduction gear in which a high output is required.
2. Description of the Prior Art
In the prior art, it is widely known to provide an speed increasing gear or a reduction gear employing an inscribed meshing planetary gear construction comprising a first shaft, an eccentric body mounted on the first shaft, an eccentric bearing mounted in the outer periphery of the eccentric body, an external-tooth gear mounted in the outer periphery of the eccentric bearing in a state where the external-tooth gear can be rotated eccentrically around the first shaft, an internal-tooth gear with which the external-tooth gear is inscribed and meshed, and a second shaft connected to the external-tooth gear through means for transmitting only the rotation component of the external-tooth gear.
An example of the prior art of this construction is shown in FIGS. 5 and 6. This prior art is constructed such that first shaft is applied as an input shaft, second shaft is applied as an output shaft and at the same time, the construction is utilized as a reduction gear by fixing the internal-tooth gear.
Eccentric bodies 3a, 3b are fitted to the input shaft 1 with a predetermined phase difference (180.degree. in this example). The eccentric bodies 3a, 3b are integrated into one body. Two external-tooth gears 5a, 5b are supported on each of these eccentric bodies 3a, 3b through eccentric bearings 4a, 4b. A plurality of inner roller holes 6 are provided in the external-tooth gears 5a, 5b. An inner pin 7 and an inner roller 8 are fitted in these roller holes.
As the eccentric bearings 4a, 4b, cylindrical roller bearings are employed in terms of demand of strength, and a part of the external-tooth gears 5a, 5b serves as the outer races thereof.
A main object of providing two external-tooth gears (in plural rows) is to increase a transmittance capacity, maintain a strength and keep a rotational balance.
External teeth 9 such as trochoidal teeth or circular teeth etc. are provided at outer circumferences of the external-tooth gears 5a, 5b. The outer teeth 9 are inscribed and meshed with the internal-tooth gear 10 fixed to a casing 12. The internal teeth of the internal-tooth gear 10 are constructed such that an outer pin 11 is loosely fitted to an inner pin hole 13 and held to be easily rotatable.
An inner pin 7 passing through the external-tooth gears 5a, 5b is tightly fixed to or fitted to a flange part 14 of the output shaft 2.
When the input shaft 1 is rotated once, the eccentric bodies 3a, 3b also rotate once. The external-tooth gears 5a, 5b oscillatebly rotate around the input shaft 1 through this one revolution of the eccentric bodies 3a and 3b. However, since the rotation is restricted by the internal-tooth gear 10, the external-tooth gears 5a, 5b almost merely perform oscillation while being inscribed with the internal-tooth gear 10.
Now, it is assumed that the number of teeth of the external-tooth gears 5a, 5b is N and the number of teeth of the internal-tooth gear 10 is N+1, then the difference between the numbers of teeth is 1. Consequently, the external-tooth gears 5a, 5b are displaced by one tooth relative to the internal-tooth gear 10 fixed to the casing 12 every time the input shaft 1 is rotated. This means that one revolution of the input shaft 1 is decelerated to a revolution of -1/N of the internal-tooth gear.
Oscillation component of the external-tooth gears 5a, 5b is absorbed by clearances between the inner roller holes 6 and the inner pins 7 and then only the revolution component is transmitted to the output shaft 2 through the inner pins 7.
In this case, the inner roller holes 6a, 6b and the inner pins 7 (inner rollers 8) form an "isokinetic inscribed meshing mechanism".
As a result, finally, a reduction of reduction ratio -1/N can be accomplished.
In the example of this prior art, the internal-tooth gear of the inscribed meshing planetary gear construction is fixed, the first shaft is an input shaft and the second shaft is an output shaft. However, a reduction gear can also be constructed by fixing the second shaft and applying the first shaft as an input shaft and the internal-tooth gear as an output shaft. Furthermore, a speed increasing gear can also be constructed by reversing these inputs and outputs.
As described above, the inner pin 7 has a function of forming an circular tooth acting as one of elements of the isokinetic inscribed meshing mechanism constructed with the inner roller holes 6a, 6b, and also has another function acting as a carrier member for transmitting a rotational force of a rotation of external-tooth gears 5a, 5b to the output shaft 2. In particular, in order to keep a superior former function, it was essential to provide inner rollers 8 capable of being freely rotated around the outer circumference of the inner pins 7. The inner roller 8 presents a problem of expensive cost due to the fact that the material must be hard and both outer and inner circumferences thereof must be coaxially and accurately machined.
In view of this fact, an idea has been proposed that the function which forms a circular tooth of one of the elements of the isokinetic inscribed meshing mechanism and another function which acts as a carrier member for transmitting a rotational force of the external-tooth gears 5a, 5b to the output shaft 2 be separated, and even if the inner roller 8 is eliminated, it has a similar performance to a mechanism having an inner roller 8.
This hypothetical structure is illustrated in FIGS. 7 and 8.
This structure comprises a means for transmitting a rotational component of the external-tooth gears, the inner pin 7 capable of constructing the isokinetic inscribed meshing mechanism relative to the inner pin holes (corresponding to the inner roller holes) 19a, 19b arranged in the external-tooth gears 5a, 5b, an annular support ring 17 receiving a rotation corresponding to the rotational component of the inner pin 7 (=the rotational component of the external-tooth gears), and a carrier pin 16 projected from the flange part 14 formed at the output shaft 2, connected and fixed to the support ring 17.
The inner pin 7 is rotatably fitted to the flange part 14 and the support ring 17 through bushes 18a, 18b. That is, since the inner pin 7 is not necessarily tightly connected to the output shaft 2 due to the presence of the carrier pin 16, it can be made to be rotatable itself, resulting in that the prior art inner roller 8 can be eliminated. The annular support ring 17 is assembled to an extremity end portion of the carrier pin 16. Since the carrier pin 16 only has the function of transmitting a rotational force of the support ring 17 to the output shaft, there are provided big through-holes 20a, 20b which do not interfere with the carrier pin 16 even if the carrier pin 16 oscillates at the corresponding portion on the external-tooth gears 5a, 5b.
Incidentally, in FIG. 8, reference numerals 15a, 15b denote bearings of the output shaft 2. Reference numeral 21 denotes an inner pin keep plate for determining an axial position of the inner pin 7. Reference numeral 23 denotes an inner pin keep bolt. Reference numeral 22 denotes a steel plate race.
It should be noted that in the inscribed meshing type planetary gear construction as described above, the reduction ratio can be freely changed merely by changing the external-tooth gears 5a and 5b, the internal-tooth gear 10, the outer pin 11 and the eccentric bodies 3a and 3b.
Therefore, there is prepared in advance a sub-series of devices (this sub-series will be hereinafter referred to as a "frame number") in which specific sets of dimensions, referred to as tie-in dimensions with respect to a mating machine determined by dimensions of the output shaft 2 and the casing 12 are categorized into small to large sizes in response to the market. That is, the devices in one sub-series all have the same output shaft size and the same casing size, regardless of reduction ratio. Additionally, the kinds of speed change ratios are systematized and prepared in advance in the same frame number to thereby enable meeting the needs of a variety of users.
Specifically, in the known arrangement, those having a reduction ratio of 1/6 to 1/119, a combination of a motor of 0.1 Kw to 132 Kw and an output torque of 0.35 kgm to 6000 kgm are prepared according to a plurality of frame numbers.
Generally, in the inscribed meshing type planetary gear construction, parts are used in common with each other in the same frame number. In this manner, only one kind of the eccentric bearings 4a and 4b have been used since they are bearings which need be produced in volume.
It is to be noted that an eccentric amount of a low reduction ratio is large whereas an eccentric amount of a high reduction ratio is small in terms of a relation-ship between the reduction ratio and the eccentric amount. Specifically, generally, for those shown in FIGS. 5 and 6, when A is the pitch radius of the internal-tooth gear, 1/N is the reduction ratio and e is eccentric amount, e=0.5 to 1.5 A/N is set.
Accordingly, in the low reduction ratio (N: small), the eccentric amount e is large, and therefore, the thickness t1 of the eccentric members 3a and 3b and the input shaft 1, and the thickness t2 of the key way are required to be secured. So, the inside diameter d2 of the eccentric bearings 4a and 4b is determined with respect to the diameter d1 of the input shaft 1. Because of this, in order to obtain the eccentric bearings 4a and 4b having a large load capacity with the aforesaid inside diameter d2, cylindrical roller bearings are generally employed as previously mentioned, and a part of the external-tooth gears 5a and 5b serves as the outer races thereof to effectively utilize space.
It is to be noted that in the case of the high reduction ratio (N: large) with the corresponding small eccentric amount e, the thicknesses t1 and t2 are needed for strength, and thus more than as needed, and the space efficiency is poor.
On the other hand, in the combination of the same motors, the higher the reduction ratio, the larger the output torque. The load of the eccentric bearings 4a and 4b also tends to be large accordingly. Therefore, since the output torque is restricted by the load capacity of the eccentric bearings 4a and 4b, in the case where within the same dimension, deep-groove ball bearings having a relatively smaller load capacity than that of the cylindrical roller bearings are used, a large torque is not provided. Under these circumstances, the deep-groove ball bearings which have a high general-use property and are low in cost cannot be used. Particularly, on the side of the high reduction ratio, the cylindrical roller bearings of high cost are often unavoidably employed to avoid the restriction by limited load capacity of the eccentric bearings.